Manufacture of electrical energy generation equipment

ABSTRACT

The invention relates to a portable electrical energy generator, its components, and manufacture of the components and generator. The generator includes a bi-polar plate stack, which is well suited for use in a fuel cell. The stack may include at least one spacer that limits compression of a membrane electrode assembly in the fuel cell. The stack may also include a polymer binder that holds the stack together and/or maintains a compression force on the membrane electrode assembly. An open cathode manifold may also provided to ease oxygen movement. High throughput and low cost manufacture of bi-polar plates is also described herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims priority under 35 U.S.C.§120 from co-pending U.S. patent application Ser. No. 11/621,897, filedJan. 10, 2007 and entitled, “PORTABLE ELECTRICAL ENERGY GENERATIONEQUIPMENT,” which claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 60/758,709, filed on Jan. 12, 2006and entitled “FUEL CELL BI-POLAR PLATE MANUFACTURING,” both of which areincorporated by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of portable electricalenergy generation equipment. In particular, the invention relates todesign and manufacture of portable fuel cells and portable fuel cellcomponents.

A fuel cell electrochemically combines hydrogen and oxygen to produceelectricity. To date, fuel cells are only commercially available inlarge-scale applications such as automobiles and industrial sizegenerators for electrical power back up. Consumer electronics devicesand other portable electrical power applications currently rely onlithium ion and similar battery technologies. Fuel cell systems thatgenerate electrical energy for portable applications such as electronicsoffer extended usage sessions, would be desirable, but are still indevelopment and not yet commercially available.

Portable fuel cells are currently encountering difficultiestransitioning from lab prototypes to consumer ready products.Manufacturing realities—such as cost, product reliably, andmanufacturing precision and repeatability—are obstructing the evolutionof portable fuel cells into viable commercial products. Portable fuelcell designs and manufacturing techniques that promote reliable and costeffective mass production of fuel cells, and their components, would bebeneficial.

SUMMARY OF THE INVENTION

The present invention relates to a portable electrical energy generator,its components, and manufacture of the components and generator. Thegenerator includes a bi-polar plate stack, which is well suited for usein a fuel cell. The stack may include at least one spacer that limitscompression of a membrane electrode assembly in the fuel cell. The stackmay also include a polymer binder that holds the stack together and/ormaintains a compression force on the membrane electrode assembly. Anopen cathode manifold may also provided to ease oxygen movement. Highthroughput and low cost manufacture of bi-polar plates is also describedherein.

In one aspect, the present invention relates to a stack for use in anelectrical energy generator. The stack includes a first bi-polar plateand a second bi-polar plate. The first bi-polar plate includes a) asubstrate, and b) a channel field formed into the substrate and locatedin a central portion of the bi-polar plate. The second bi-polar plateincludes a) a substrate, and b) a second channel field formed into thesecond bi-polar plate substrate and located in a central portion of thesecond bi-polar plate. The stack also includes at least one spacerattached to perimeter portion of the first bi-polar plate and attachedto perimeter portion of the second bi-polar plate. The at least onespacer is configured to form a socket between the first bi-polar plateand the second bi-polar plate. The stack further includes a membraneelectrode assembly disposed in the socket.

In another aspect, the present invention relates to a method ofmanufacturing a stack for use in portable electrical energy generator.The method includes receiving a first bi-polar plate and a secondbi-polar plate. The method also includes attaching at least one spacerto the first bi-polar plate and the second bi-polar plate to form asocket between the first bi-polar plate and the second bi-polar plate.The method further includes disposing a membrane electrode assemblywithin the socket. The method additionally includes compressing themembrane electrode assembly. The method also includes limitingcompression of the membrane electrode assembly using the at least onespacer.

In yet another aspect, the present invention relates to a stack thatincludes a first bi-polar plate, a second bi-polar plate, and a membraneelectrode assembly disposed between the first bi-polar plate and thesecond bi-polar plate. The stack also includes at least one polymerelement configured to attach the first bi-polar plate to the secondbi-polar plate and to maintain a compression force on the membraneelectrode assembly.

In still another aspect, the present invention relates to a stackincluding multiple bi-polar plates that each has a cathode channel fieldformed into the bi-polar plate. The stack also includes an open cathodemanifold configured to open between the cathode channel field and anenvironment around the stack.

In another aspect, the present invention relates to a stack. The stackincludes a first bi-polar plate including a) a substrate, and b) ananode channel field formed into a first face of the substrate andlocated in a central portion of the bi-polar plate, and c) a cathodechannel field formed into a second face of the substrate and located ina central portion of the bi-polar plate. The stack also includes asecond bi-polar plate including a) a substrate, and b) a an anodechannel field formed into the second bi-polar plate substrate andlocated in a central portion of the second bi-polar plate. The stackfurther includes a third bi-polar plate including a) a substrate, and b)a cathode channel field formed into the third bi-polar plate substrateand located in a central portion of the third bi-polar plate. The stackadditionally includes at least one spacer attached to perimeter portionof the second face of the first bi-polar plate and attached to perimeterportion of the second bi-polar plate, wherein the at least one spacer isconfigured to form a first socket between the first bi-polar plate andthe second bi-polar plate. The stack also includes at least one spacerattached to perimeter portion of the first face of the first bi-polarplate, and attached to perimeter portion of the third bi-polar plate,wherein the at least one spacer in the between the first bi-polar plateand the third bi-polar plate is configured to form a second socketbetween the first bi-polar plate and the third bi-polar plate. The stackfurther includes a membrane electrode assembly disposed in the firstsocket and a membrane electrode assembly disposed in the first socket.

In another aspect, the present invention relates to a stack. The stackincludes a first bi-polar plate including a) a first sheet with a firstbi-polar plate channel field formed through the first sheet and b) asecond sheet attached to the first sheet and including a second channelfield formed through the second sheet. The stack also includes a secondbi-polar plate including a) a third sheet with a third bi-polar platechannel field formed through the third sheet and b) a fourth sheetattached to the fourth sheet and including a fourth channel field formedthrough the fourth sheet.

These and other features of the present invention will be described inthe following description of the invention and associated figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an outer top perspective view of a fuel cell inaccordance with a specific embodiment of the present invention.

FIG. 1B illustrates a simplified cross sectional view of a fuel cellstack used in the fuel cell of FIG. 1A in accordance with one embodimentof the present invention.

FIG. 1C illustrates a top perspective view of a stack of bi-polar platesin accordance with another specific embodiment of the present invention.

FIG. 2 shows a bi-polar plate in accordance with one embodiment of thepresent invention.

FIG. 3A shows a fuel cell stack in accordance with another embodiment ofthe present invention.

FIG. 3B shows a top view of a bi-polar plate with attached spacers inaccordance with a specific embodiment of the present invention.

FIG. 3C shows a perspective view of a bi-polar plate with attachedspacers in accordance with a specific embodiment of the presentinvention.

FIG. 3D shows an exploded view of the spacers and bi-polar plate of FIG.3C.

FIG. 3E shows a cross sectional perspective view of the spacers attachedto the bi-polar plate of FIG. 3C.

FIG. 4A shows a series of sealing lines between a spacer and bi-polarplate in accordance with a specific embodiment of the present invention.

FIG. 4B shows a series of sealing lines in accordance with anotherspecific embodiment of the present invention.

FIG. 4C shows a fillet weld between bi-polar plate and spacer, which isapplied at a corner between bi-polar plate and spacer.

FIG. 5 shows a bi-polar plate including multiple flat sheets inaccordance with one embodiment of the present invention.

FIG. 6 shows clad manufacturing of a bi-polar plate substrate inaccordance with one embodiment of the present invention.

FIG. 7A shows the clad sheet output in FIG. 6 after stamping inaccordance with a specific embodiment of the present invention.

FIGS. 7B-7E various suitable bi-polar plate geometries made usingvarious manufacturing techniques described herein.

FIG. 8 shows an exploded view of a fuel cell stack in accordance withanother embodiment of the present invention.

FIG. 9 shows a bi-polar plate in accordance with another embodiment ofthe present invention.

FIG. 10 shows a method for manufacturing a fuel cell in accordance withone embodiment of the present invention.

FIG. 11 illustrates schematic operation for a reformed fuel cell systemin accordance with a specific embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail with reference to a fewpreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

FIGS. 1A-1C show a fuel cell 20 in accordance with specific embodimentsof the present invention.

Referring first to FIG. 1A, fuel cell 20 electrochemically convertshydrogen and oxygen to water, generating electrical energy (andsometimes heat) in the process. Ambient air readily supplies oxygen. Apure or direct oxygen source may also be used.

Hydrogen provision uses a working supply. The hydrogen supply mayinclude a direct hydrogen supply or hydrogen from a reformed fuelsupply. A direct hydrogen supply employs a pure source, such ascompressed hydrogen in a pressurized container, or a solid-hydrogenstorage system, such as a metal-based hydrogen storage device. Areformed hydrogen supply processes a fuel to produce hydrogen. The fuelacts as a hydrogen carrier, is manipulated to separate hydrogen, and mayinclude a hydrocarbon fuel, hydrogen bearing fuel stream, or any otherhydrogen fuel such as ammonia. One suitable reformed fuel cell system isdescribed below with respect to FIG. 11. Current popular hydrocarbonfuels include methanol, ethanol, gasoline, propane and natural gas.Liquid fuels offer high energy densities and the ability to be readilystored and transported. The water often forms as a vapor, depending onthe temperature of fuel cell 20. For some fuel cells, theelectrochemical reaction may also produce carbon dioxide as a byproduct.

Several fuel cell classes are suitable for use herein. In oneembodiment, fuel cell 20 is a reformed methanol fuel cell (RMFC). Thepresent invention may also apply to a solid oxide fuel cell (SOFC), aphosphoric acid fuel cell (PAFC), a direct methanol fuel cell (DMFC), ora direct ethanol fuel cell (DEFC). Fuel cell 20 includes componentsspecific to each architecture, as one of skill in the art willappreciate. A DMFC or DEFC receives and processes a fuel. Morespecifically, a DMFC or DEFC receives liquid methanol or ethanol,respectively, channels the fuel into the fuel cell stack and processesthe liquid fuel to separate hydrogen for electrical energy generation.For a DMFC, channel fields in the bi-polar plates distribute liquidmethanol instead of hydrogen. The hydrogen catalyst then includes asuitable anode catalyst for separating hydrogen from methanol. Theoxygen catalyst includes a suitable cathode catalyst for processingoxygen or another suitable oxidant used in the DMFC, such as peroxide.In general, the hydrogen catalyst is also commonly referred to as ananode catalyst in other fuel cell architectures and may comprise anysuitable catalyst that removes hydrogen for electrical energy generationin a fuel cell, such as directly from the fuel as in a DMFC. In general,the oxygen catalyst may include any catalyst that processes an oxidantin used in fuel cell 20. The oxidant may include any liquid or gas thatoxidizes the fuel and is not limited to oxygen gas as described above.An SOFC, PAFC or MCFC may also benefit from inventions described herein,for example. In this case, fuel cell 20 comprises an anode catalyst,cathode catalyst, anode fuel and oxidant according to a specific SOFC,PAFC or MCFC design.

Fuel cell 20 is well suited for use with micro fuel cell systems. Amicro fuel cell generates dc voltage, and may be used in a wide varietyof applications. For example, electrical energy generated by a microfuel cell may power a notebook computer or a portable electricalgenerator carried by military personnel. In one embodiment, the presentinvention provides ‘small’ fuel cells that are configured to output lessthan 200 watts of power (net or total). Fuel cells of this size arecommonly referred to as ‘micro fuel cells’ and are well suited for usewith portable electronics devices. In one embodiment, the fuel cell isconfigured to generate from about 1 milliwatt to about 200 Watts. Inanother embodiment, the fuel cell generates from about 5 Watts to about60 Watts. The fuel cell system may be a stand-alone system, which is asingle package that produces power as long as it has access to a) oxygenand b) hydrogen or a hydrogen source such as a hydrocarbon fuel. Onespecific portable fuel cell package produces about 20 Watts or about 45Watts, depending on the number of cells in the stack.

Fuel cell 20 includes a fuel cell stack 60. Referring to FIG. 1B, fuelcell stack 60 includes a set of bi-polar plates 44 and a set of membraneelectrode assembly (MEA) layers 62. Two MEA layers 62 neighbor eachbi-polar plate 44. With the exception of topmost and bottommost membraneelectrode assembly layers 62 a and 62 b, each MEA 62 is disposed betweentwo adjacent bi-polar plates 44. For MEAs 62 a and 62 b, top and bottomend plates 64 a and 64 b include a channel field (a set of channels on asurface) on the face neighboring an MEA 62.

In one embodiment, each bi-polar plate 44 is formed from one or moresubstantially flat plates and includes channel fields on oppositesurfaces of the bi-polar plate. Thickness for each bi-polar plate istypically less than about 5 millimeters, and compact fuel cells forportable applications may employ bi-polar plates thinner than about 2millimeters. In a specific embodiment, each bi-polar plate 44 includesmultiple layers that include more than one sheet of metal. Severalsuitable bi-polar plate designs are described below.

Collectively, in stack 60, bi-polar plates 44 distribute hydrogen andoxygen in stack 60. Gaseous hydrogen distribution to the hydrogen gasdistribution layer in the MEA occurs via a hydrogen channel field on abi-polar plate, while oxygen distribution to the oxygen gas distributionlayer in the MEA occurs via an oxygen channel field. In one embodiment,a single bi-polar plate dually distributes hydrogen and oxygen: onechannel field distributes hydrogen while a channel field on the oppositeface of the bi-polar plate 44 distributes oxygen. In another embodiment,a single bi-polar plate only distributes hydrogen or oxygen and theadjacent MEAs are oriented accordingly.

In electrical terms, the anode includes the hydrogen gas distributionlayer, hydrogen catalyst and a bi-polar plate. The anode acts as thenegative electrode for fuel cell 20 and conducts electrons that arefreed from hydrogen molecules so that they can be used externally, e.g.,to power an external circuit or stored in a battery. In electricalterms, the cathode includes the oxygen gas distribution layer, oxygencatalyst and an adjacent bi-polar plate. The cathode represents thepositive electrode for fuel cell 20 and conducts the electrons back fromthe external electrical circuit to the oxygen catalyst, where they canrecombine with hydrogen ions and oxygen to form water.

In fuel cell stack 60, the assembled bi-polar plates 44 are connected inseries to add electrical potential gained in each layer of the stack.The term ‘bi-polar’ refers electrically to a bi-polar plate (whethermechanically comprised of one plate or multiple pieces and/or plates)sandwiched between two membrane electrode assembly 62 layers. In a stackwhere plates 44 are connected in series, a bi-polar plate 44 may act asboth a negative terminal for one adjacent (e.g., above) membraneelectrode assembly and a positive terminal for a second adjacent (e.g.,below) membrane electrode assembly arranged on the opposite surface ofthe bi-polar plate.

The number of bi-polar plates 44 and MEA layers 62 in each set may varywith design of fuel cell stack 60. Stacking parallel layers in fuel cellstack 60 permits efficient use of space and increased power density forfuel cell 20 and a fuel cell package including fuel cell 20. In oneembodiment, each membrane electrode assembly 62 produces 0.7 V and thenumber of MEA layers 62 and bi-polar plates 44 are selected to achieve adesired voltage. Fuel cell 20 size and layout may also be tailored andconfigured to output a given power.

While the present invention will mainly be discussed with respect to PEMfuel cells, it is understood that the present invention may be practicedwith other fuel cell architectures. The main difference between fuelcell architectures is the type of ion conductive membrane used. Inanother embodiment, fuel cell 20 is phosphoric acid fuel cell thatemploys liquid phosphoric acid for ion exchange. Solid oxide fuel cellsemploy a hard, non-porous ceramic compound for ion exchange and may besuitable for use with the present invention. Other suitable fuel cellarchitectures include alkaline and molten carbonate fuel cells, forexample.

In a PEM fuel cell, the hydrogen catalyst separates the hydrogen intoprotons and electrons. The ion conductive membrane blocks the electrons,and electrically isolates the chemical anode (hydrogen gas distributionlayer and hydrogen catalyst) from the chemical cathode. The ionconductive membrane also selectively conducts positively charged ions.Electrically, the anode conducts electrons to a load (electrical energyis produced) or battery (energy is stored). Meanwhile, protons movethrough the ion conductive membrane. The protons and used electronssubsequently meet on the cathode side, and combine with oxygen to formwater. The oxygen catalyst in the oxygen gas distribution layerfacilitates this reaction. One common oxygen catalyst comprises platinumpowder thinly coated onto a carbon paper or cloth. Many designs employ arough and porous catalyst to increase surface area of the platinumexposed to the hydrogen and oxygen.

For product and reactant communication, fuel cell 20 includes one ormore intake and outlet manifolds that communicate gases with thebi-polar plates 44. Each manifold delivers a product or reactant gas toor from the fuel cell stack 60. More specifically, each manifolddelivers a gas between a vertical manifold created by stacking bi-polarplates 44 (FIG. 1C) and plumbing external to fuel cell 20.

As shown in FIG. 1A, fuel cell 20 includes two anode manifolds 84 and86. Inlet hydrogen manifold 84 is disposed on top end plate 64 a,couples to an inlet line or conduit to receive hydrogen gas, and opensto an inlet hydrogen manifold 102 (FIG. 1C) that is configured todeliver inlet hydrogen gas to a channel field 72 on each bi-polar plate44 in stack 60. Outlet manifold 86 receives outlet gases from an anodeexhaust manifold 104 (FIG. 1C) that is configured to collect wasteproducts from the anode channel fields 72 of each bi-polar plate 44.Outlet manifold 86 may provide the exhaust gases to the ambient spaceabout the fuel cell. In another embodiment, manifold 86 provides theanode exhaust to a line that transports the unused hydrogen back to afuel processor.

Fuel cell 20 includes two cathode manifolds: an inlet cathode manifoldor inlet oxygen manifold 88, and an outlet cathode manifold or outletwater/vapor manifold 90. Inlet oxygen manifold 88 is disposed on top endplate 64 a, couples with an inlet conduit to receive ambient air, andopens to an oxygen manifold 106 (FIG. 1C) that is configured to deliverinlet oxygen and ambient air to a channel field 72 on each bi-polarplate 44 in stack 60. In another embodiment, fuel cell 20 does notinclude inlet oxygen manifold 88 but instead includes an open cathodemanifold that eases fuel cell system oxygen movement. Outlet water/vapormanifold 90 receives outlet gases from a cathode exhaust manifold 108(FIG. 1C) that is configured to collect water (typically as a vapor)from the cathode channel fields 72 on each bi-polar plate 44.

As shown in FIG. 1A, manifolds 84, 86, 88 and 90 include molded channelsthat each travel along a top surface of end plate 64 a from theirinterface from outside the fuel cell to a manifold in the stack. Eachmanifold or channel acts as a gaseous communication line for fuel cell20 and may comprise a molded channel in plate 64 or a housing of fuelcell 20. Other arrangements to communicate gases to and from stack 60are contemplated, such as those that do not share common manifolding ina single plate or structure.

Referring to FIG. 1B, top and bottom end plates 64 a and 64 b providemechanical protection for stack 60. End plates 64 also hold the bi-polarplates 44 and MEA layers 62 together, and apply pressure across theplanar area of each bi-polar plate 44 and each MEA 62. End plates 64 mayinclude steel or another suitably stiff material. Bolts 82 a-d connectand secure top and bottom end plates 64 a and 64 b together. In anotherembodiment (FIG. 8), stack 60 includes polymer elements that hold thestack together and maintain pressure across the planar area of eachbi-polar plate 44 and each MEA 62.

FIG. 1C illustrates a top perspective view of a stack of bi-polar plates(with the top two plates labeled 44 a and 44 b) in accordance with oneembodiment of the present invention. Bi-polar plate 44 a is a singlesubstantially flat plate with channel fields 72 carved into on oppositefaces 75 of the plate 44.

Functionally, bi-polar plate 44 a) delivers and distributes reactantgases to the gas diffusion layers and their respective catalysts, b)maintains separation of the reactant gasses from one another between MEAlayers 62 in stack 60, c) exhausts electrochemical reaction byproductsfrom MEA layers 62, and d) includes gas intake and gas exhaust manifoldsfor gas delivery to other bi-polar plates 44 in the fuel stack 60.

FIG. 2 shows a bi-polar plate 44 in accordance with one embodiment ofthe present invention. Bi-polar plate 44 includes a substantially flatprofile with top and bottom opposing faces 75 a and 75 b and a channelfield 72 or “flow field” on each opposing face.

Structurally, bi-polar plate 44 has a substantially flat profile andincludes opposing top and bottom faces 75 a and 75 b and a number ofsides 78. Faces 75 are substantially planar with the exception ofchannels 76 formed as troughs into substrate 89. Sides 78 compriseportions of bi-polar plate 44 proximate to edges of bi-polar plate 44between the two faces 75. As shown in FIGS. 1C and 3B, bi-polar plate 44is roughly quadrilateral.

Bi-polar plate 44 includes a channel field 72 or “flow field” on eachface of plate 44. Each channel field 72 includes one or more channels 76formed into the substrate 89 of plate 44 such that the channel restsbelow a surface 91 on each face 75 of plate 44. Each channel field 72distributes one or more reactant gasses to an active area for the fuelcell stack 60. Bi-polar plate 44 includes an anode channel field 72 a onthe anode face 75 a of bi-polar plate 44 that distributes hydrogen,while a cathode channel field on opposite cathode face 75 b distributesoxygen. For fuel cell stack 60, each channel field 72 is configured toreceive a reactant gas from an intake manifold 102 or 106 and configuredto distribute the reactant gas to a gas diffusion layer in the MEA. Eachchannel field 72 also collects reaction byproducts for exhaust from fuelcell 20. When bi-polar plates 44 are stacked together in fuel cell 60,adjacent plates 44 sandwich an MEA layer 62 such that the anode face 75a from one bi-polar plate 44 neighbors a cathode face 75 b of anadjacent bi-polar plate 44 on an opposite side of an MEA layer 62.

From a top or bottom perspective, each plate has a central portion 85(FIG. 2) and a perimeter portion 87 (FIGS. 1C and 2). Central portionsof bi-polar plate 44 include substantially planar portions of a bi-polarplate that include a channel 76 or channel field 72, or portions thatare generally away from the sides 78 of plate 44. Perimeter portions 87of bi-polar plate 44 include any portions of plate 44 proximate to aside 78 or edge of the substrate included in plate 44. External portionsof bi-polar plate 44 often do not include a channel field 72.

Substrate 89 refers to the material used in bi-polar plate 44. Suitablematerials for used in bi-polar plate 44 include: a metal (stainlesssteel, copper, aluminum, titanium, etc.), graphite, polymer (filled orunfilled), ceramic, or a composite of these materials. Although bi-polarplate 44 is shown with one substrate, bi-polar plates of the presentinvention may include multiple substrates and materials (e.g., see FIG.5).

One or more coatings may also be applied onto substrate 89 to improvechemical resistance and/or electrical conductance. To prevent corrosion,a metal may be coated with a protective coating such as gold, silver,niobium, etc. Other suitable coatings include PEMCOAT FC7 as provided byIneos Technologies of Cheshire, UK on a stainless steel base-platematerial; a copper sheet with clad stainless steel on each side may becoated with PEMCOAT FC7.

In one embodiment, a bi-polar plate 44 is considered ‘flat’ when surface91 is about the same thickness in the central portion 85 (e.g., betweenchannels 76 in field 72) as the perimeter portions 87. In other words,the surface 75 a to surface 75 b thickness of plate 44 is consistentbetween central portion 85 and perimeter portions 87.

The manifold on each plate 44 is configured to deliver a gas to achannel field on a face of the plate 44 or receive a gas from thechannel field 72. The manifolds for bi-polar plate 44 include aperturesor holes in substrate 89 that, when combined with manifolds of otherplates 44 in a stack 60, form an inter-plate 44 gaseous communicationmanifold (such as 102, 104, 106 and 108). Thus, when plates 44 arestacked and their manifolds substantially align, the manifolds permitgaseous delivery to and from each plate 44.

In one embodiment, bi-polar plates 44 in stack 60 each include one ormore heat transfer appendages 46 (FIG. 1C). Each heat transferappendages 46 provides conductive heat transfer between external andinternal portions of a fuel cell stack, which permits external thermalmanagement of internal portions of fuel cell stack 60. Morespecifically, appendage 46 may be used to heat or cool internal portionsof fuel cell stack 60 such as internal portions of each attachedbi-polar plate 44 and any neighboring MEA layers 62. Heat transferappendage 46 is laterally arranged outside channel field 72. In oneembodiment, appendage 46 is disposed on a perimeter portion 87 ofbi-polar plate 44.

Peripherally disposing heat transfer appendage 46 allows heat transferbetween inner portions of plate 44 and the externally disposed appendage46 via the plate substrate 89. In one embodiment, heat transferappendage 46 is integral with substrate material 89 in plate 44.Integral in this sense refers to material continuity between appendage46 and plate 44. Heat may travel to or from the heat transfer appendage46. In other words, appendage 46 may be employed as a heat sink orsource. Thus, heat transfer appendage 46 may be used as a heat sink tocool internal portions of bi-polar plate 44 or an MEA 62.

FIG. 3A shows a fuel cell stack 60 in accordance with another embodimentof the present invention. Stack 60 includes spacers 100 that separateadjacent bi-polar plates 44 in the stack. FIG. 3B shows a top view of aspacer 100 and bi-polar plate 44 in accordance with a specificembodiment of the present invention.

In this case, MEA 62 includes a kapton layer 102 that separates acathode diffusion layer 104 and an anode diffusion layer 106. In oneembodiment, fuel cell 20 is a low volume ion conductive membrane (PEM)fuel cell suitable for use with portable applications such as consumerelectronics. A PEM fuel cell comprises an MEA 62 that carries out theelectrical energy generating an electrochemical reaction. The PEM MEA 62includes a hydrogen catalyst, an oxygen catalyst, and an ion conductivemembrane 102 that a) selectively conducts protons and b) electricallyisolates the hydrogen catalyst from the oxygen catalyst. Anode diffusionlayer 106 contains the hydrogen catalyst and allows the diffusion ofhydrogen therethrough. Cathode diffusion layer 104 contains the oxygencatalyst and allows the diffusion of oxygen and hydrogen protonstherethrough. Typically, the ion conductive membrane separates thehydrogen and oxygen gas distribution layers. In chemical terms, theanode comprises the hydrogen gas distribution layer and hydrogencatalyst, while the cathode comprises the oxygen gas distribution layerand oxygen catalyst. In a specific embodiment, MEA 62 includes a modelnumber P1000 or P2000 available from PEMEAS of Frankfurt, Germany. OtherMEAs are also suitable for use herein.

A membrane electrode assembly is often compliant. Under-compression ofMEA 62 may lead to performance degradation of the membrane electrodeassembly; over-compression of MEA 62 may lead to MEA damage. In oneembodiment, fuel cell 20 includes one or more spacers that contain MEA62 compression within a desired range.

Spacers 100 a and 100 b are configured to maintain a socket 110 betweenbi-polar plates 44 a and 44 b. Socket 110 refers to a volume betweenbi-polar plates 44 a and 44 b. In this case, socket 100 is defined bydepth 112 (FIG. 3A) and planar area 114 (FIG. 3B). Spacers 100 alsoresemble a frame when viewed from the top in FIG. 3B. Socket 110 issized to receive MEA 62.

Kapton layer 102 fits between adjacent spacers 100 a and 100 b. When thestack has been assembled and compressed, spacers 100 a and 100 bcompress and hold kapton layer 102, which holds MEA 62 in place.

Fuel cell stack 60 compresses bi-polar plates 44 and MEAs. For the stack60 shown in FIG. 1A, bolts 82 apply compression forces to the stack 60.In another embodiment, polymer adhesion and attachment to and betweenbi-polar plates 44 holds stack 60 together and maintains compressionforces in stack 60. This embodiment will be described in further detailbelow with respect to FIG. 8.

Spacers 100 include a rigid material with an elastic modulus largeenough to prevent further compression on MEA 62 once the spacers are incontact. In one embodiment, spacer 100 includes a material with anelastic modulus greater than about 1 GPa. Many metals, polymers andceramics are suitable for use in this regard. Spacer 100 may include: ametal (stainless steel, copper, aluminum, titanium, etc.), graphite,grafoil, polymer (polyimide, FEP, LCP, etc.), ceramic, or a composite ofthese materials. Other materials may also be used. In one embodiment,spacer 100 includes a high temperature plastic that can withstand acontinuous temperature corresponding to the maximum operatingtemperature of fuel cell 20. The operating temperature may range fromabout 80 degrees Celsius to about 200 degrees Celsius, depending on thetype of fuel cell. For a 200 degrees Celsius maximum operatingtemperature, suitable thermoplastics include polyetheretherketone(PEEK), polyethersulfone, polyphenylene ether (PPE), andpolytetrafluoroethylene (PTFE).

As shown in FIGS. 3A and 3C, two spacers 100 b and 100 c are attached toeither side of a flat bi-polar plate 44 b. FIG. 3D shows an explodedview of the spacers 100 b and 100 c and bi-polar plate 44 b. FIG. 3Eshows a cross sectional perspective view of the spacers 100 b and 100 cattached to bi-polar plate 44 b.

Returning back to FIG. 3A, during and after assembly of stack 60,spacers 100 a and 100 b control the compression thickness of MEA 62.More specifically, when stack 60 is compressed, spacers 100 a and 100 bprovide a hard stop for the vertical distance between adjacent plates 44and a hard stop for the compression of MEA 62 in a fuel cell stack. Inthis case, the compression thickness of MEA 62 after assembly of stack60 is roughly the depth 112 provided by spacers 100 a and 100 b betweenopposing surfaces 91 on plates 44 a and 44 b (e.g., the kapton layer 102may add to depth 112 and the compression thickness of MEA 62).

Spacers 100 separate manufacture of two features of a bi-polar plate44—the flow field 72 and socket 110—so that these can be createdseparately. This opens the number of manufacturing methods for eachfeature and for of these parts. Separate manufacture of bi-polar plateand socket (and their respective 2-D profiles, as opposed to bi-polarplate needing a 3-D manufacturing process): increases the number ofpermissible fabrication approaches, and lowers bi-polar plate and stackcost. In many cases, spacers 100 permit improved control of thecompression thickness of MEA 62 using a low cost, highly dimensionallycontrollable, and well-sealed manufacturing process for spacer 100and/or bi-polar plate 44.

By contrast, in FIG. 1B, the socket that determined MEA 62 thickness wasa part of, and recessed into, the adjacent bi-polar plates 44.Fabricating multiple recesses in a plate (one for the socket, and asecond for the channels in the socket) requires 3-D manufacturingcapability, and quality control of this recessed dual-depth isdifficult. In addition, fabricating this recessed depth can increase thecost of a bi-polar plate and limits the methods by which the bi-polarplate flow fields can be manufactured.

Thus, by adding the spacers 100 during fabrication and then bonding eachto a flat bi-polar plate 44, manufacture of stack 60 and fuel cell 20becomes less expensive. At the least, the use of spacers 100 avoids theneed for manufacturing raised features on each bi-polar plate 44 to forma socket 110 for an MEA, which simplifies the manufacture of each plate.Again, devoid of spacers 100, bi-polar plate 44 often needs two depthsof machining and material removal from substrate 89 (one for the socketdepth 112 and another for the channel 76 depth). With spacers 100,bi-polar plate 44 only needs a single depth of machining for the channel76 depth. Because each spacer 100 and bi-polar plate 44 are bothsubstantially a two-dimensional part, each with a particular thickness,the number of permissible manufacturing methods for creating spacer 100and plate 44 increases, which increases manufacturing flexibility,increases options for reliable manufacturing, and reduces cost. Methodsfor 2-D manufacture of spacer 100 and plate 44 may include, for example,water-jet cutting, laser cutting, photochemically etching, machining,electro-discharge machining, stamping, molding, etc. A single-depthdesign of bi-polar plate 44 also permits the flow field 72 to be createdthrough several simpler 2-D manufacturing methods, such as:photochemical etching, electrochemically grinding, machining and 2-Dmilling, stamping, coining, molding, etc.

Numerous attachment techniques may be used during manufacture to attachspacer 100 to bi-polar plate 44. As one of skill in the art willappreciate, the materials used for spacer 100 and bi-polar plate 44 willaffect the permissible attachment options. Depending on the plate 44material and spacer 100 material, the bonding methods may include:laser-welding, brazing, ultrasonic welding, radio frequency welding,heat sealing, diffusion bonding or brazing, for example. Increasing thenumber of options for attachment improves manufacture by potentiallyreducing costs, selecting a manufacturing technique that increasesreliability, etc.

In one embodiment, one or both spacers 100 a and 100 b are permanentlyattached to a bi-polar plate 44 using bonding processes such asdiffusion bonding, laser welding, brazing or adhesion. One suitableadhesive is Viton THA-3000 as provided by Thermodyne of Sylvania, Ohio.This adhesive attachment functions as a mechanical feature that allowsfor high speed robotic handling of the bonded bi-polar plates, and alsofunctions as a gas sealant. Other suitable adhesives include: Vitoncaulk or Fluorodyn Caulk as provided by Thermodyne; Epoxy, Master BondEP46HT-1 or Epoxy, Master Bond EP17HT as provided by Master Bond,Hackensack of NJ.

In another embodiment, fuel cell 20 includes an adhesive hydraulicsealant that attaches spacer 100 to bi-polar plate 44. The hydraulicsealant provides: a) a hermetic seal between spacer 100 and bi-polarplate 44 and; b) a hermetic seal between spacer 100 and MEA 62. Thehydraulic sealant also offers chemical resistance—at fuel cell operatingtemperatures—to chemicals used the fuel cell, such as phosphoric acid. Asuitable hydraulic sealant is Krytox sealant manufactured by DuPont ofWilmington Del. for example, which has enough “tack” to keep thebi-polar plate 44 and spacer 100 joined to each other duringmanufacture, which also permits high-speed robotic handling.

The attachment between bi-polar plate 44 and spacer 100 may also providesealing. The particular sealing technique used may depend on the tomaterials bi-polar plate 44 and spacer 100, as one of skill in the artwill appreciate. For instance, a copper spacer 100 may be laser-weldedto a copper bi-polar plate 44. Weld paths may be used to seal onemanifold from the other. Another attachment uses a thin film of PTFE(Polytetrafluoroethylene) placed between a metal plate and metal frame.This polymer layer bonds the two metal layers when placed under heat andpressure. In another embodiment, spacer 100 is made of a polymer andlaminated to a metal flat bi-polar plate 44 using a heat-sealing method.

One or more sealing lines may define the contact and sealing portionsbetween bi-polar plate 44 and spacer 100. FIG. 4A shows a series ofsealing lines 130, as dashed lines, in accordance with a specificembodiment of the present invention. Bi-polar plate 44 shows the cathodeface with a cathode flow field 72.

Sealing lines 130 include laser weld paths that seal the anode manifolds102 and 104 from the cathode flow field 72. A first sealing line 130 aincludes a butt (or lap) weld that is perpendicular to the seam betweenspacer 100 and bi-polar plate 44, and seals the external perimeter ofthe stack along the planar sides. A second sealing line 130 b includes afillet weld that perimetrically borders inlet hydrogen manifold 102 andseals the hydrogen manifold 102 from the cathode flow field 72; a thirdsealing line 130 c includes a fillet weld that borders outlet hydrogenmanifold 104 and seals outlet hydrogen manifold 104 from the cathodeflow field 72.

Numerous alterations to the design using spacers 100 are permissible.FIG. 4B shows the sealing lines 140 for a spacer 100 a and bi-polarplate 44 in accordance with another specific embodiment of the presentinvention.

In this case, spacer 100 a includes a smaller planar area than bi-polarplate 44 along sealing lines 140. This permits the use of a fillet weldalong sealing lines 140. FIG. 4C shows a fillet weld 135 betweenbi-polar plate 44 and spacer 100 a, which is applied at a corner 137between bi-polar plate 44 and spacer 100 a. The smaller planar area ofspacer 100 a permits a corner 137 to exist along any sealing linesbetween bi-polar plate 44 and spacer 100 a. For example, this permits afillet weld to be used for all three sealing lines 130 a, 130 b and 130c of FIG. 4A.

As mentioned above, spacer 100 allows a bi-polar plate to be machinedwith one depth for each face (e.g., just one depth for the channels onthat face). In another embodiment, fuel cell stack manufacture andassembly is further simplified by forming a bi-polar plate from two(initially) separate sheets.

FIG. 5 shows a bi-polar plate 44 d in accordance with another embodimentof the present invention. Bi-polar plate 44 d includes two relativelyflat sheets 150 a and 150 b. Each flat sheet 150 includes a channelfield whose channels extend through the sheet from one face of the sheetto the other face. For example, flat sheet 150 a includes anode channels152 that pass through sheet 150 a, while flat sheet 150 b includescathode channels 154 that pass through sheet 150 b.

Sheets 150 a and 150 b are assembled such that channels 152 and channels154 do not overlap. The solid portions of one sheet 150 then act as abottom for channels of the other sheet, as shown. Sheets 150 a and 150 bare attached using any suitable technique, and sealed, according totheir respective materials. Suitable materials for sheets 150 a and 150b include any material listed above with respect to substrate 89 ofbi-polar plate 44.

Because each sheet 150 is a two-dimensional part, with a particularthickness, the number of permissible manufacturing methods for creatingeach sheet 150 opens, which increases manufacturing flexibility,increases options for reliable manufacturing, and reduces cost. Methodsfor manufacture of sheet 150 may include, for example, water-jetcutting, laser cutting, photochemical etching, machining,electrochemical grinding, 2-D milling, electro-discharge machining,stamping, coining, molding, etc.

The simplified bi-polar plate designs permit 2-D manufacturing ofbi-polar plates 44, sheets 150, and/or spacers 100. This permits the useof high throughput and low-cost manufacture techniques.

For example, FIG. 6 shows clad manufacturing of a bi-polar plate 44 inaccordance with one embodiment of the present invention. Bi-polar platemanufacture in this case includes two steps: a clad step (FIG. 6), and achannel-forming step (techniques may vary and FIG. 7A shows the outputof this second step) that together output a two-dimensional bi-polarplate.

As shown in FIG. 6, three layers are provided to cladding rolls 170: aninner layer 172, a top layer 174, and bottom layer 176. Inner layer 172forms the main substrate 89 for bi-polar plate 44; copper is suitable inmany embodiments. Top player 174 and bottom layer 176 form platedsurfaces on inner layer 172 and improve chemical resistance and/orconductivity of bi-polar plate 44. Gold is suitable for use with copper,and sometimes includes a thin layer of nickel between the gold andcopper to prevent the gold from diffusing into the copper. Claddingrolls 170 cold-roll compress the layers 170, 172 and 174 to output asingle clad sheet 178 with the inlet layers formed together into anintegral plate. Clad sheet 178 resembles substrate 89 in bi-polar plate44 before any channels or other feature have been added.

Channels 72 and other features in bi-polar plate 44 are then formed intoclad sheet 178. In one embodiment, a stamping process is used to producechannels 72 in bi-polar plate 44. Stamping permits “roll forming”,shearing and punching for high volume manufacturing. Stamping may beused to produce sheets 150 of bi-polar plate 44 as shown in FIG. 7A. Astamping process may also be used to create spacers 100. Othermanufacturing techniques suitable to form channels in clad sheet 178include coining and find blanking, for example.

Clad sheet 178 may include a large number of bi-polar plates 44 afterstamping. FIG. 7A shows clad sheet 178 after stamping in accordance witha specific embodiment of the present invention. In this case, thissegment of clad sheet 178 includes 20 bi-polar plates 44. Obviously,clad sheet 178 may be continuous sheet with many more bi-polar plates44. Portable fuel cells typically include bi-polar plates 44 with aplanar area less than about 200 cm squared. Clad sheet 178 may be aswide as a meter, which allows even more bi-polar plates 44 across itswidth.

The cladding and stamping process permit roll-to-roll manufacturing.This provides high throughput and inexpensive manufacture of thousandsof bi-polar plates 44. The cladding and stamping processes may alsoproduces precise manufacturing tolerances (e.g., thickness of bi-polarplate 44) relative to milling operations.

Geometry of a bi-polar plate may vary. In some cases, channel geometrymay be affected by the manufacturing technique used to make the bi-polarplate. FIGS. 7B-7E various bi-polar plate and channel geometriessuitable for use herein, and made using various manufacturingtechniques.

FIG. 7B shows a bi-polar plate 44 p made from rolling and coiningprocesses in accordance with a specific embodiment of the presentinvention. Bi-polar plate 44 p includes channels 72 p with pointed andsharp features produced in a coining process.

FIG. 7C shows a bi-polar plate 44 q made from photochemical etching inaccordance with a specific embodiment of the present invention. Bi-polarplate 44 q includes channels 72 q whose dimensions are rounded todesired dimensions using the better spatial control provided byphotochemical etching.

FIG. 7D shows a bi-polar plate 44 r made from photochemical etching inaccordance with another specific embodiment of the present invention. Inthis case, the plate includes cathode channels 72 r that are larger thanthe anode channels 72 s. The cathode channels 72 r provide lowresistance airflow paths that are configured for, and well suited foruse with, an open manifold design (see FIG. 9) that allows air to besupplied directly through channels 72 r using a fan or blower.

FIG. 7E shows a bi-polar plate 44 s made from rolling and stampingprocesses in accordance with a specific embodiment of the presentinvention. Bi-polar plate 44 s includes contiguous channel dimensions 72t with less pointed and sharp features, as would be resultant from astamping process.

As mentioned above, the MEA is compressed and plates are held togetherafter stack assembly is finished. FIG. 8 shows an exploded view of afuel cell 20 in accordance with one embodiment of the present invention.Fuel cell 20 includes polymer elements 160 that extend through bi-polarplates 44 of stack 60.

Polymer elements 160 are configured to attach two adjacent bi-polarplates 44 in stack 60 when the stack is assembled. FIG. 8 shows theexploded view before the stack is vertically assembled. After verticalassembly, energy is provided to polymer elements 160 to cause slightmelting and deformation to the polymer in elements 160, therebyattaching: top plate 64 a to the topmost bi-polar plate 44, all adjacentbi-polar plates 44 in stack 60, the bottommost bi-polar plate 44 instack 60 to bottom plate 64 b, and bottom plate 64 b to manifold plate164.

In this case, the same polymer elements 160 pass from the top of stack60 to the bottom and extend through each bi-polar plate 44 in stack 60,resembling rivets or bolts that pass through the entire stack. Althoughnot shown, fuel cell 20 may include a receiving polymer layer or ringdisposed on the top side of end plate 64 a; this receiving polymer layeror ring includes a number of holes configured to mate with the distalends of polymer elements 160. Energy input into the polymer elements andreceiving polymer layer or ring then attaches the bottom plate 164 tothe receiving polymer layer or ring disposed on the top side of endplate 64 a, similar to bolts that pass from top to bottom as shown inFIG. 1A.

In another embodiment, stack 60 includes smaller polymer elements 160that only blind two adjacent bi-polar plates 44. Cumulatively, when allthe bi-polar plates 44 are assembled in stack 60, the smaller polymerelements 160 hold the entire stack 60 together and maintain anycompression forces applied thereto during the energy input.

Polymer elements 160 may include any polymer that deforms under externalenergy, such as ultrasonic input, to form a shape suitable to attachmultiple but polar plates. The polymer elements, after deformation, alsoinclude suitable rigidity and strength to prevent movement betweenadjacent bi-polar plates 44. In one embodiment, polymer elements 160include a moldable polymer, such as liquid crystal polymer (LCP) orpolyphenol polymer (PPS). Other polymers are suitable for use. Forexample, numerous thermoplastics are suitable for use with ultrasonicwelding.

The input energy may include any single or combination of energy sourcessuitable to reshape the polymer elements 160. Heat and/or ultrasonicwelding are suitable for use. For example, ultrasonic welding may beused to join two adjacent bi-polar plates using polymer elements 160. Inone embodiment, the polymer elements 160 employ ultrasonic concentrationfeatures (such as triangles and grooves) that reduce the energy and/ortime needed to start and complete melting. The ultrasonic concentrationfeatures may also include features and joints that promote energydirection and/or joint shear. An energy director joint design may beused and includes one or more raised triangular or pointed beads ofmaterial molded on one of the joint surfaces. One function of the energydirector is to concentrate energy to rapidly initiate softening andmelting of the joining surfaces. A tongue and groove may also be appliedon the joining surfaces to prevent flash, both internally andexternally, and provide alignment. A step joint, textured surface,criss-cross, chisel or other energy directing geometry may also be usedto increase efficiency or efficacy of the ultrasonic welding.

Typically, compression of stack 60 occurs after the layers have beenvertically assembled. Energy input into polymer elements 160 may thenoccur while the entire stack 60 is compressed. When the energy has beenremoved and polymer elements 160 reshaped by the input energy, there-solidified polymer elements 160 then hold stack 60 in its compressedstate. For manufacturing perspective, this manufacturing method providesrepeatable and reliable compression on stack 60 for hundreds orthousands of fuel cells being manufactured.

The number of polymer elements 160 may vary. In one embodiment, fuelcell 20 includes between about 2 and about 30 polymer elements perbi-polar plate. As shown in FIG. 8, each of these polymer elements 160may pass through multiple bi-polar plates 44 in stack 60. In a specificembodiment, fuel cell 20 includes between about 4 and about 16 polymerelements per bi-polar plate.

FIG. 9 shows a bi-polar plate 180 in accordance with another embodimentof the present invention. Bi-polar plate 180 includes an open inletcathode manifold 182 and an open outlet cathode manifold 184.

A fuel cell stack 60 using bi-polar plate 180 then includes multiplebi-polar plates 180 stacked vertically such that open cathode manifold182 extends vertically through the entire stack 60 to service eachbi-polar plate 180 of the stack.

The open manifolds 182 and 184 simplify oxygen movement through a fuelcell stack in a portable fuel cell system. Open inlet cathode manifold182 opens to the environment around the stack 50 and fuel cell 20 andpermits a fan 189 to blow air 185 into open cathode manifold 182. Theair then passes through each bi-polar plate 180 in stack 60, and to openoutlet cathode manifold 184. The heated and humid air exhausted fromfuel cell stack 60 may then be provided into the ambient environmentwithout any additional plumbing. In another embodiment, bi-polar plate180 does not include an open outlet cathode manifold 184, but includes aclosed cathode manifold that outlets the oxygen to plumbing for use in afuel processor.

By contrast, inlet cathode manifold 106 of FIG. 1C increases flowresistance and typically relies on a compressor to push air and oxygenthrough the inlet plumbing to manifold 106, through inlet cathodemanifold 106, through the cathode channels 72 in all bi-polar plates 44of stack 60, and at of stack 60 and bi-polar plate 20. The compressor istypically large and heavy for a portable fuel cell system.

FIG. 10 shows a method 300 for manufacturing a fuel cell in accordancewith one embodiment of the present invention.

Method 300 begins by receiving a bi-polar plate (302). In oneembodiment, construction of the bi-polar plate is outsourced to a vendorin the bi-polar plates are received from the vendor. In anotherembodiment, bi-polar plate manufacture precedes method 300. Numeroussuitable techniques for mass production of bi-polar plates weredescribed above. For example, the bi-polar plate may be made using highthroughput techniques such as cladding and stamping. A bi-polar platemay also be formed in a single molding, stamping, machining or MEMsprocess of a single metal sheet, for example.

One or more spacers are then attached to each bi-polar plate (304).Suitable attachment techniques were described above with respect toFIGS. 3-4 and may include welding, brazing, and polymer-to-polymerwelding, for example. In some cases, one or more sealing lines may beformed between the spacer and bi-polar plate to regulate movement ofreactants and products in a fuel cell stack. A membrane electrodeassembly is then inserted into a socket formed by the spacers andbi-polar plate (306).

Steps 302-306 may be repeated in parallel for multiple plates, spacersand membrane electrode assemblies. In a specific embodiment, the stackshown in FIG. 1C is assembled vertically one bi-polar plate at a time.Commonly, the membrane electrode assembly is disposed within the socketafter the first spacer is attached to a first bi-polar plate, and beforethe spacer a second bi-polar plate laid overtop the MEA and firstbi-polar plate.

The bi-polar plates in the stack are then attached to each other, alongwith compression of the stack and membrane electrode assemblies includedtherein (308). In one embodiment, all the plates in the stack areattached and compressed in a single step, such as using bolts that screwto a desired compression pressure on the MEA. Another single stepattachment and compression uses polymer binding as described above withrespect to FIG. 8. In this case, a desired pressure on stack ismaintained while the polymer is welded to its new shape. In anotherembodiment, bi-polar attachment occurs one plate at a time between eachpair of adjacent bi-polar plates. Polymer binders as described above aresuitable for use in this regard.

The amount of compression on the stack may vary. In one embodiment, thestack is compressed to a desired socket depth 112 between bi-polarplates 44 (see FIG. 3A). The MEA 62 manufacturer may specify the socketdepth 112. Other socket depths 112 may be used. The cumulative heightfor spacers 100 a and 100 b may be selected to provide a socket depthcorresponding to a certain fraction of the MEA 62 height beforecompression. In one embodiment, the cumulative height for spacers 100 aand 100 b is between about 0.7 and about 0.9 of the MEA 62 height beforecompression. In a specific embodiment, the cumulative height for spacers100 a and 100 b is between about 0.75 and about 0.85 of the MEA 62height before compression. This may or may not include thickness ofkapton layer 102. Other parameters may be used to determine the socketdepth 112.

As mentioned above, fuel cell 20 may be used in a reformed fuel cellsystem (RMFC). FIG. 11 illustrates schematic operation for the fuel cellsystem 10 in accordance with a specific embodiment of the presentinvention.

Fuel storage device 16 stores methanol or a methanol mixture as ahydrogen fuel 17. An outlet of storage device 16 includes a connector 23that mates with a mating connector on a package 11. In this case, a fuelcell package 11 includes the fuel cell 20, fuel processor 15, and allother balance-of-plant components except the cartridge 16. In a specificembodiment, the connector 23 and mating connector form a quickconnect/disconnect for easy replacement of cartridges 16. The matingconnector communicates methanol 17 into hydrogen fuel line 25, which isinternal to package 11 in this case.

Line 25 divides into two lines: a first line 27 that transports methanol17 to a heater/heater 30 for fuel processor 15 and a second line 29 thattransports methanol 17 for a reformer 32 in fuel processor 15. Lines 25,27 and 29 may comprise channels disposed in the fuel processor (e.g.,channels in metals components) and/or tubes leading thereto.

Flow control is provided on each line 27 and 29. Separate pumps 21 a and21 b are provided for lines 27 and 29, respectively, to pressurize eachline separately and transfer methanol at independent rates, if desired.A model 030SP-S6112 pump as provided by Biochem, N.J. is suitable totransmit liquid methanol on either line in a specific embodiment. Adiaphragm or piezoelectric pump is also suitable for use with system 10.A flow restriction may also provided on each line 27 and 29 tofacilitate sensor feedback and flow rate control. In conjunction withsuitable control, such as digital control applied by a processor thatimplements instructions from stored software, each pump 21 responds tocontrol signals from the processor and moves a desired amount ofmethanol 17 from storage device 16 to heater 30 and reformer 32 on eachline 27 and 29. In another specific embodiment shown, line 29 runs inletmethanol 17 across or through a heat exchanger that receives heat fromthe exhaust of the heater 30 in fuel processor 15. This increasesthermal efficiency for system 10 by preheating the incoming fuel (toreduce heating of the fuel in heater 30) and recuperates heat that wouldotherwise be expended from the system.

Air source 41 delivers oxygen and air from the ambient room through line31 to the cathode in fuel cell 20, where some oxygen is used in thecathode to generate electricity. Air source 41 may include a pump, fan,blower or compressor, for example. High operating temperatures in fuelcell 20 also heat the oxygen and air.

In the embodiment shown, the heated oxygen and air is then transmittedfrom the fuel cell via line 33 to a regenerator 36 (also referred toherein as a ‘dewar’) of fuel processor 15, where the air is additionallyheated (by the heater, while in the dewar) before entering heater 30.This double pre-heating increases efficiency of the fuel cell system 10by a) reducing heat lost to reactants in heater 30 (such as fresh oxygenthat would otherwise be near room temperature when combusted in theheater), and b) cooling the fuel cell during energy production. In thisembodiment, a model BTC compressor as provided by Hargraves, N.C. issuitable to pressurize oxygen and air for fuel cell system 10.

A fan 37 blows cooling air (e.g., from the ambient room) over fuel cell20.

Fuel processor 15 receives methanol 17 and outputs hydrogen. Fuelprocessor 15 comprises heater 30, reformer 32, boiler 34 and regenerator36. Heater 30 (also referred to herein as a burner when it usescatalytic combustion to generate heat) includes an inlet that receivesmethanol 17 from line 27. In a specific embodiment, the burner includesa catalyst that helps generate heat from methanol. In anotherembodiment, heater 30 also includes its own boiler to preheat fuel forthe heater.

Boiler 34 includes a boiler chamber having an inlet that receivesmethanol 17 from line 29. The boiler chamber is configured to receiveheat from heater 30, via heat conduction through walls in monolithicstructure between the boiler 34 and heater 30, and use the heat to boilthe methanol passing through the boiler chamber. The structure of boiler34 permits heat produced in heater 30 to heat methanol 17 in boiler 34before reformer 32 receives the methanol 17. In a specific embodiment,the boiler chamber is sized to boil methanol before receipt by reformer32. Boiler 34 includes an outlet that provides heated methanol 17 toreformer 32.

Reformer 32 includes an inlet that receives heated methanol 17 fromboiler 34. A catalyst in reformer 32 reacts with the methanol 17 toproduce hydrogen and carbon dioxide; this reaction is endothermic anddraws heat from heater 30. A hydrogen outlet of reformer 32 outputshydrogen to line 39. In one embodiment, fuel processor 15 also includesa preferential oxidizer that intercepts reformer 32 hydrogen exhaust anddecreases the amount of carbon monoxide in the exhaust. The preferentialoxidizer employs oxygen from an air inlet to the preferential oxidizerand a catalyst, such as ruthenium or platinum that is preferential tocarbon monoxide over hydrogen.

Regenerator 36 pre-heats incoming air before the air enters heater 30.In one sense, regenerator 36 uses outward traveling waste heat in fuelprocessor 15 to increase thermal management and thermal efficiency ofthe fuel processor. Specifically, waste heat from heater 30 pre-heatsincoming air provided to heater 30 to reduce heat transfer to the airwithin the heater. As a result, more heat transfers from the heater toreformer 32. The regenerator also functions as insulation for the fuelprocessor. More specifically, by reducing the overall amount of heatloss from the fuel processor, regenerator 36 also reduces heat loss frompackage 10 by heating air before the heat escapes fuel processor 15.This reduces heat loss from fuel processor 15, which enables cooler fuelcell system 10 packages.

Line 39 transports hydrogen (or ‘reformate’) from fuel processor 15 tofuel cell 20. In a specific embodiment, gaseous delivery lines 33, 35and 39 include channels in a metal interconnect that couples to bothfuel processor 15 and fuel cell 20. A hydrogen flow sensor (not shown)may also be added on line 39 to detect and communicate the amount ofhydrogen being delivered to fuel cell 20. In conjunction with thehydrogen flow sensor and suitable control, such as digital controlapplied by a processor that implements instructions from storedsoftware, fuel processor 15 regulates hydrogen gas provision to fuelcell 20.

Fuel cell 20 includes a hydrogen inlet port that receives hydrogen fromline 39 and includes a hydrogen intake manifold that delivers the gas toone or more bi-polar plates and their hydrogen distribution channels. Anoxygen inlet port of fuel cell 20 receives oxygen from line 31; anoxygen intake manifold receives the oxygen from the port and deliversthe oxygen to one or more bi-polar plates and their oxygen distributionchannels. A cathode exhaust manifold collects gases from the oxygendistribution channels and delivers them to a cathode exhaust port andline 33, or to the ambient room. An anode exhaust manifold 38 collectsgases from the hydrogen distribution channels, and in one embodiment,delivers the gases to the ambient room.

In the embodiment shown, the anode exhaust is transferred back to fuelprocessor 15. In this case, system 10 comprises plumbing 38 thattransports unused hydrogen from the anode exhaust to heater 30. Forsystem 10, heater 30 includes two inlets: an inlet configured to receivefuel 17 and an inlet configured to receive hydrogen from line 38. In oneembodiment, gaseous delivery in line 38 back to fuel processor 15 relieson pressure at the exhaust of the anode gas distribution channels, e.g.,in the anode exhaust manifold. In another embodiment, an anode recyclingpump or fan is added to line 38 to pressurize the line and return unusedhydrogen back to fuel processor 15.

In one embodiment, fuel cell 20 includes one or more heat transferappendages 46 that permit conductive heat transfer with internalportions of a fuel cell stack. In a specific heating embodiment asshown, exhaust of heater 30 in fuel processor 15 is transported to theone or more heat transfer appendages 46 in fuel cell 20 during systemstart-up to expedite reaching initial elevated operating temperatures inthe fuel cell 20. The heat may come from hot exhaust gases or unburnedfuel in the exhaust, which then interacts with a catalyst disposed inproximity to a heat transfer appendage 46. In a specific coolingembodiment, fan 37 blows cooling air over the one or more heat transferappendages 46, which provides dedicated and controllable cooling of thestack during electrical energy production.

In one embodiment, in operation under steady state conditions, methanolfuel 17 moves into reformer 32 where it is converted to reformate gas39. This reformate gas is fed into a fuel cell anode 43 where apercentage of available fuel (e.g., hydrogen) is consumed; thereafterthe remaining fuel depleted reformate is fed into a catalytic heater 30located in fuel processor 15. In the catalytic heater 30 (or burner),the remaining fuel is oxidized and heat is released into reformer 32 tosupply heat of formation for fuel 17. The fuel then exits to the burnerexhaust. Air is fed via a compressor into the fuel cell cathode 45 whereoxygen is consumed proportionally to the fuel consumed at the anode. Theoxygen-depleted, steam-enriched, air then exits the cathode 45 and isfed into the fuel processor burner 30 to oxidize the remaining fuel 17mentioned above; since the air enters the fuel cell 20 first, it gainsheat thereby reducing the heat load on burner 30. The burner 30 exhaustis finally fed into a recuperator where heat from the exhaust gas isdumped into the liquid fuel 17 inlet to the reformer. This heat exchangeallows for pre-vaporized fuel 17 to enter the reforming chamber fromline 29, thereby reducing the heat duty on burner 30 and increasing thesystem 10 efficiency. In another specific embodiment, hot exhaust of theheat exchanger is fed into a second burner located in thermalcommunication with fuel cell 20; a separate blower or fan feeds air intothe fuel cell burner with the goal of oxidizing any remaining fuel.Additional air may be supplied to the fuel cell thermal appendages viafan 37. Finally, the fuel cell cooling air and the fuel cell burnerexhaust gasses converge into a single stream; the system exhaust.Further temperature dilution may be obtained by addition of a furtherair stream supplied by a system-cooling fan or blower. Finally, thesystem exhaust may be passed over exhaust section of the cartridgehousing; exhaust filters or sensors may be included on the exhaustsection of the cartridge housing.

On startup, the operation may differ from steady state operation. In oneembodiment, a fuel igniter is activated until it is at about 300-500degrees Celsius. Methanol 17 is fed into burner 30 and when it contactsthe igniter, it flash boils and the methanol vapor mixes with air toform a combustible mixture, which is ignited by the burner catalyst.Fuel 17 and air are fed into the burner in order to heat it up tooperating temperatures, e.g., about 240-300 degrees Celsius. The hotburner exhaust impinges on the fuel cell heat transfer appendages 46;thereby dumping heat from the burner exhaust gas stream into fuel cell20. When the reformer temperature is at a desired point, and the fuelcell 20 temperature rises above the condensing point of reformate gas,fuel is fed into the reformer, whereupon it converts into a hydrogenrich gas stream (reformate.) The reformate passes through the fuel cellanode 43 where a small amount of hydrogen is consumed at the anode(e.g., a small load applied to keep the average fuel cell voltage lessthan 0.75V/cell to prevent carbon corrosion.) Reformate then is fed backinto the burner where some fuel is oxidized (rich mixture), releasingheat into the fuel processor. Finally, the hot exhaust passes throughthe recuperator and into a fuel cell burner, whereupon the remainingfuel is oxidized by addition of oxygen from the startup blower. Once thefuel cell and fuel processors are at their desired temperatures, thesystem reverts to steady state operation.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. For example, although the present invention hasdescribed stack assembly without mention of location techniques betweenplates, one of skill in the art is aware of numerous fixturingtechniques suitable for use herein. It is therefore intended that thescope of the invention should be determined with reference to theappended claims.

1. A stack for use in an electrical energy generator, the stackcomprising: a first bi-polar plate including a) a substrate, and b) achannel field formed into the substrate and located in a central portionof the bi-polar plate; a second bi-polar plate including a) a substrate,and b) a second channel field formed into the second bi-polar platesubstrate and located in a central portion of the second bi-polar plate;at least one spacer attached to perimeter portion of the first bi-polarplate and attached to perimeter portion of the second bi-polar plate,wherein the at least one spacer is configured to form a socket betweenthe first bi-polar plate and the second bi-polar plate; and a membraneelectrode assembly disposed in the socket.
 2. The stack of claim 1,wherein the at least one spacer is configured to produce a socket depthbetween the first bi-polar plate and the second bi-polar plate that isless than a thickness for the membrane electrode assembly beforeassembly of the stack.
 3. The stack of claim 2, wherein stack iscompressed after assembly of the stack and the at least one spacer issized to limit compression of the membrane electrode assembly.
 4. Thestack of claim 2, wherein the socket depth is between about 0.7 andabout 0.9 times the thickness for the membrane electrode assembly beforeassembly of the bi-polar plate stack.
 5. The stack of claim 4, whereinthe socket depth is between about 0.75 and about 0.85 times thethickness for the membrane electrode assembly before assembly of thebi-polar plate stack.
 6. The stack of claim 4, wherein the firstbi-polar plate includes a central thickness between a first surface ofthe substrate and an opposite surface of the substrate in the centralportion that is about the same thickness between the first surface andthe opposite surface in the perimeter portion.
 7. The stack of claim 1,wherein the first bi-polar plate includes a) a first sheet with thefirst bi-polar plate channel field formed through the first sheet and b)a second sheet attached to the first sheet and including a secondchannel field formed through the second sheet.
 8. The stack of claim 1,wherein the spacer has a smaller planar area than the first bi-polarplate.
 9. The stack of claim 8, wherein the spacer has a larger crosssectional area for a planar feature than a planar feature on the firstbi-polar plate.
 10. The stack of claim 9, wherein the spacer and thefirst bi-polar plate both include a metal and are joined using a filletweld.
 11. The stack of claim 1, wherein the first bi-polar plate isattached to the spacer using an adhesive hydraulic sealant.
 12. Thestack of claim 1, wherein each of the first and second bi-polar platesis formed from a single substantially flat substrate and includeschannel fields on opposite surfaces of the substrate.
 13. The stack ofclaim 12, wherein channels of the channel fields are formed as troughsinto opposite surfaces of the substrate.
 14. A stack for use in anelectrical energy generator, the stack comprising: a first bi-polarplate formed of a single substantially flat substrate having a firstchannel field formed into the first bi-polar plate substrate and locatedin a central portion of the first bi-polar plate; a second bi-polarplate formed of a single substantially flat substrate having a secondchannel field formed into the second bi-polar plate substrate andlocated in a central portion of the second bi-polar plate; at least onespacer attached to perimeter portion of the first bi-polar plate andattached to perimeter portion of the second bi-polar plate, wherein theat least one spacer is configured to form a socket between the firstbi-polar plate and the second bi-polar plate; and a membrane electrodeassembly disposed in the socket.
 15. The stack of claim 14, wherein theat least one spacer is configured to produce a socket depth between thebi-polar plates that is less than a thickness for the membrane electrodeassembly before assembly of the stack.
 16. The stack of claim 15,wherein the socket depth is between about 0.7 and about 0.9 times athickness of the membrane electrode assembly before assembly of thestack.
 17. The stack of claim 14, wherein the at least one spacer isattached to the bi-polar plates using an adhesive hydraulic sealant. 18.The stack of claim 14, wherein the spacers comprise a rigid materialwith an elastic modulus large enough to prevent further compression onthe membrane electrode assembly once the stack is assembled.
 19. Thestack of claim 18, wherein the elastic modulus is greater than about 1GPa.
 20. The stack of claim of claim 14, wherein the spacers comprise amaterial selected from the group consisting of a metal, polymer, andceramic.